Method and device for high resolution acousto-optic programmable filtering in the infrared region

Abstract

The subject matter of the invention is a method of high-resolution acousto-optic programmable filtering in the infrared region of an incident optical wave. To that end it proposes the use of a birefringent acousto-optic crystal whereof the propagation speed of acoustic waves is slow, such as compounds of mercury, which acousto-optic crystal comprises, on one of its faces, a piezoelectric transducer designed to generate a transverse acoustic wave with wave vector whereof the energy propagates according to the same axis but in the opposite direction to the energy of the incident optical wave, knowing that the optical wave resulting from the acousto-optic interaction between the incident optical wave and the acoustic wave with wave vector is diffracted perpendicularly or almost perpendicularly to the direction of the incident optical wave.

1. A device for spectral high-resolution acousto-optic programmable filtering in the infrared region of an incident optical wave comprising:
 a birefringent acousto-optic crystal, from the tetragonal crystal class, having a slow acoustic wave propagation velocity along the [ 110 ] axis, 
 a piezoelectric transducer disposed on a surface of the birefringent acousto-optic crystal, 
 means for inputting an incident ordinary optical wave into said birefringent acousto-optic crystal, in a plan of said crystal containing the axis [ 001 ] and [ 110 ], 
 means for generating in the birefringent acousto-optic crystal a transverse acoustic wave with wave vector, in said plan of said crystal containing the axis [ 001 ] and [ 110 ], through said piezoelectric transducer, disposed so that:
 the energy of the transverse acoustic wave propagates along a same axis but in an opposite direction to the energy of said incident optical wave, and 
 an extraordinary optical wave, resulting from the acousto-optic interaction between said incident optical wave and said transverse acoustic wave, which is diffracted with wave vector, substantially perpendicularly to the direction of said incident optical wave. 
 
 
     
     
       2. The device according to  claim 1 , wherein the acousto-optic crystal is made of calomel, and designed so that the direction of said incident optical wave and of the energy of the said acoustic wave with wave vector make an angle close to 60° with the axis of said acousto-optic crystal. 
     
     
       3. The device according to  claim 1 , wherein the birefringent acousto-optic crystal comprises a compound of mercury. 
     
     
       4. The device according to  claim 1 , further comprising a reflective surface disposed so that said diffracted optical wave is re-diffracted substantially collinearly with the direction of said incident optical wave after reflection on said reflective surface. 
     
     
       5. The device according to  claim 4 , wherein the reflective surface is a mirror fixed to the birefringent acousto-optic crystal. 
     
     
       6. The device according to  claim 5 , wherein said piezoelectric transducer configured to generate a transverse acoustic wave is a transducer placed on a face of the birefringent acousto-optic crystal opposite to an input face of the aforesaid incident optical wave. 
     
     
       7. The device according to  claim 6 , wherein the normal direction to the plane of the piezoelectric transducer makes an angle close to 10° with respect to the axis of the acousto-optic crystal.